Field of the Invention and Related Art Statement
This invention relates to a rubber reinforcement using an amorphous iron-base alloy filament as a cord stock.
More particularly, the invention proposes developmental results that the service durability of tires is largely improved by using the above reinforcement in a belt layer, a carcass ply or a chafer layer of radial tires or a breaker layer of bias tires, and that the cord weight used can be reduced by the properties inherent to the amorphous alloy such as high strength, low specific gravity and the like to thereby design the weight-saving of the tire under the same casing strength.
Tires are required to have high level performances on the running service life, high speed running property, safety and the like. For this purpose, pneumatic tires using steel cords are widely used.
Since steel cord exhibits a low reduction of the breaking tenacity due to heat history as compared with organic fiber cords, high service durability is maintained even when the tire is continuously run at a high speed for a long time, so that such a steel cord is primarily used in tires for passenger cars and long-distance transportation trucks.
In such a steel cord, however, there are some drawbacks such as reduction of strength due to the occurrence of rust, reduction of strength due to the reduction of filament section resulted from a phenomenon of rubbing filaments with each other during the running (or fretting phenomenon), corrosion fatigue breakage resulting from water or the like in rubber, and so on.
In this connection, amorphous alloys have been studied because they have excellent properties such as high strength, corrosion resistance, abrasion resistance and so on. Particularly, it is expected to rapidly enhance the durable life if amorphous iron-base alloy filaments containing small amounts of Cr, Mo, Ni and the like, which are able to develop a high corrosion resistance, can be used as a tire cord material instead of the steel cord. At present, the practicability of such as amorphous alloy is mainly progressed in the field of electric and magnetic materials, and the technology for manufacturing the same is fairly advanced, but the form of the resulting alloy is mainly a very thin ribbon.
Considering the application of the amorphous alloy to the tire, the twisting of the ribbon as a tire cord material is difficult and the stress concentration is conspicuous in the ribbon edge portion, so that the ribbon of the amorphous alloy cannot be effectively used in the tire. This is a reason why the application of the amorphous alloy to the tire is backward in spite that this alloy is generally excellent in the strength and corrosion resistance.
Lately, there has been established a production technology where an amorphous iron-base alloy filament having a circular section is relatively stably obtained as a continuous filament by jet-spinning molten metal into a refrigerant carrier as disclosed in Japanese Patent laid open No. 57-52,550, No. 57-134,248 and No. 57-161,128. As a result the applicability of such a filament to tires is largely developed, and various fundamental examinations are made as disclosed in Japanese Patent laid open No. 57-160,702. Moreover, the filaments obtained by jet-spinning into the refrigerant carrier as described above certainly have high strength, high Young's modulus, high fatigue properties and high corrosion resistance, but tend to be fairly poor in the toughness as compared with the existing piano wire (steel).
That is, this filament is inferior in strength after the bending deformation, strength at kinking and the twisting property to piano wire, which is considered due to the fact that there is existent no plastic elongation in stress-strain curve (or so-called S--C curve) during the elongation deformation, and practically causes various problems in the application to tires.
Further, the filament as spun is poor in sectional roundness, and particularly the diameter thereof changes in the longitudinal direction to cause the unevenness of diameter, at where stress may be locally concentrated to lead the breakage.
When these filaments are twisted to form a cord, it is generally required to ensure form stability and flaring resistance to the cord by subjecting the filament to a preliminary working at a form ratio corresponding to the twisting pitch of the cord. For this purpose, the preliminary working for the formation of wavy form is carried out by passing the filament through rod portions of several millimeters in diameter under flexing several times to give a fairly large strain to the filament.
However, the filaments as spun by jetting into refrigerant carrier frequently cause breakage during twisting because of no plastic deformation region and poor toughness. Further, even if the cord is successfully formed by twisting of the filaments, there is a risk of causing the filament breakage during subsequent tire running due to a large local slide deformation portion produced by poor toughness and size unevenness, particularly non-uniform deformation in twisting. These facts become a serious obstacle in the application of the filament to tires.
In order to apply the cord obtained by twisting the amorphous iron-base alloy filaments to tires, therefore, it is required to improve fundamental properties of the filament as well as the twisting property thereof and avoid the occurrence of the breakage during tire running. For this purpose, it is a subject matter to attain high levels of toughness, roundness and dimensional stability of the filament.